1. Field of the Invention
The present invention relates to a fluid dynamic bearing assembly, and more particularly, to a fluid dynamic bearing assembly included in a motor to thereby generate dynamic pressure.
2. Description of the Related Art
A small spindle motor used in a hard disk drive (HDD) is generally provided with a fluid dynamic bearing assembly, and a bearing clearance formed between a shaft and a sleeve of the fluid dynamic bearing assembly is filled with a lubricating fluid such as oil. The oil filling the bearing clearance generates fluid dynamic pressure while being compressed, thereby rotatably supporting the shaft.
That is, the fluid dynamic bearing assembly generally generates dynamic pressure through spiral shaped grooves in an axial direction and herringbone shaped grooves in a circumferential direction, thereby promoting stability in the rotational driving of the spindle motor.
Meanwhile, in accordance with the recent increase in capacity of hard disk drives, a technical problem in which vibrations generated during the driving of the spindle motor should be reduced has been caused. That is, in order to allow the hard disk drive to be driven without an error due to vibrations generated during the driving of the spindle motor, the demand for an improvement in the performance of the fluid dynamic bearing assembly included in the spindle motor has been increased.
In addition, in order to improve the performance of the fluid dynamic bearing assembly, there is a need to increase an interval (that is, a length of a bearing span) between the herringbone shaped grooves to move a rotating center upwardly, thereby reducing vibrations generated during the driving of the spindle motor.
However, there is a limitation in increasing the interval (that is, the length of the bearing span) between the herringbone shaped grooves. In other words, there is a limitation in increasing the length of the bearing span without increasing a height of the hard disk drive (in a state in which the hard disk drive has a constant height of 2.5 inches).